RNAi-dependent Polycomb repression controls transposable elements in Tetrahymena

Area of Science:

• Epigenetics
• Molecular Biology
• Genetics

Background:

• RNA interference (RNAi) and Polycomb repression are crucial for transcriptional gene silencing.
• These pathways are known to be conserved across many species and often function coordinately.
• Their precise interplay, particularly in the context of repetitive elements, remains an area of active investigation.

Purpose of the Study:

• To investigate the roles of RNAi and Polycomb repression in regulating germline-specific sequences in Tetrahymena thermophila.
• To determine the impact of impaired RNAi-dependent Polycomb repression on transposable element (TE) activity.
• To explore the relationship between noncoding RNA (ncRNA) and messenger RNA (mRNA) production in silenced and activated sequences.

Main Methods:

• Utilizing Tetrahymena thermophila mutants deficient in the RNAi-dependent Polycomb repression pathway.
• Analyzing transcriptional activation of germline-specific internally eliminated sequences (IESs), many of which are TE-related.
• Monitoring germline TE mobilization.
• Assessing the transition between ncRNA and mRNA production.

Main Results:

• Mutants lacking RNAi-dependent Polycomb repression exhibited significant transcriptional activation of germline IESs, including TE-related sequences.
• Germline TE mobilization dramatically increased in these mutant strains.
• A switch from ncRNA to mRNA production was observed upon transcriptional activation of TE-related sequences, and vice versa for silencing.

Conclusions:

• The interplay between RNAi and Polycomb repression is essential for the epigenetic silencing of transposable elements in the germline.
• This coordinated regulatory mechanism is likely a conserved phenomenon with an ancestral role in controlling TE activity.
• The balance between ncRNA and mRNA production is influenced by cotranscriptional processing, RNAi, and Polycomb repression.